Trousers, such as jeans, have belt loops that are stitched onto the waistband at predetermined intervals. The loops are stitched either manually or automatically depending on the manufacturing plant and machinery setup.
In manual belt loop stitching, an operator advances the waistband by hand through a stitching station of a sewing machine, places a belt loop over the waistband, and stitches the belt loop. This type of belt loop stitching is expensive, time-consuming and labor intensive. An automated belt loop stitching setup therefore has become more desirable.
In one automated system, indicia marks corresponding to the desired belt loop positions are placed on the waistband. The stitching machinery senses the marks by appropriate sensing systems and automatically stitches the belt loops onto the waistbands where a mark has been sensed. This system requires an extra step, i.e., marking the waistband, thus raising production and other attendant costs.
In the automated belt loop stitching operation disclosed in U.S. Pat. No. 4,555,999 to Conner, marks are not placed on the waistband, thus overcoming the marking drawback of other prior art systems. In Conner, the operator places the waistband at the stitching station beginning at the rear seam, and then stitches a belt loop. The machine automatically indexes the waistband counterclockwise to the end while counting the distance with a stepper motor control unit. The machine then reverses machine direction and indexes to the correct loop positions while stopping waistband movement intermittently for belt loop stitching based on the measured distance of the entire waistband.
Although the Conner apparatus automates belt loop attachment, it has some drawbacks because 1) the indexed positions must be calculated symmetrically from the rear seam, and 2) the trousers must be reversibly moved through the apparatus, first in one direction, followed by movement in the reverse direction.
It would be more desirable to use known reference points which are formed integral to the trousers for correlating the belt loop positions on the waistband. Such reference points would desirably include the waistband seams. Because the seams are formed integral with the trousers, there is no need to apply separate indicia as noted above. Because belt loop attachment positions are correlated with known reference points such as seams it would not be necessary to calculate distance based on the time consuming, reversing movement such as disclosed in Conner.
During production, known variables such as the detected position of a seam and the required number of belt loops would be correlated. As the waistband moves through a stitching station, belt loops could be stitched at intermittent intervals without requiring complex waistband measurements such as the reversible waistband movement disclosed in Conner. Additionally, any detection means would preferably be simple, using electromechanical apparatus that register the bulge of a seam or other integrally formed structure rather than complex electronic sensing apparatus such as disclosed in Conner.
In the device disclosed in the copending '336 parent application, the waistband is incrementally and automatically moved into belt loop attachment positions at the stitching station without being reversibly moved through the stitching station. An indexer clamp engages the waistband of the trousers and the indexer clamp moves downward from the stitching station so as pull the trouser through the stitching station. The presence of seams are detected, and the waistband attachment positions are correlated for belt loop attachment positions relative to the detected position of the seam.
A stepper motor is drivingly connected to the indexer clamp for accurate displacement of the waistband through the stitching station. In one illustrated aspect of the invention, a pivotally mounted lever engages the waistband. The lever pivots upward when a seam passes thereunder, and a signal generator generates a signal to a controller indicative of the presence of a seam. An inner guide roller engages the inside portion of a waistband before the stitching station. Typically, the operator inputs to the controller the number of belt loops which will be stitched onto the waistband. A production run of that type of waistband to be stitched then commences.
Also, as the waistband is pulled through the stitching station, the tension may vary because of the amount of material between the sewing machine bed and the indexer clamp. It has been found desirable if consistent tension could be placed on the waistband each time a loop has been sewn.
Also, at times, the waistband sensing component comprising the lever creates friction as it drags along the waistband as the waistband is advanced. Depending on the seam construction, the lever arm friction may increase error in the registration of seams. A sensor which does not create undue friction is more accurate and is therefore preferred.